My earlier U.S. Pat. No. 4,857,380 describes a foam reinforced article such as a surfboard or airplane wing, with honeycomb sheets at the top and bottom of the article and with fibrous layers at opposite faces of each honeycomb sheet. Foamed polymer material such as urethane foam, penetrates the article. The foam lies in cells of the honeycomb sheets, lies in the reinforcing fibrous layers at opposite faces of each honeycomb sheet, and fills the space between the fibrous sheets at the top and bottom honeycomb layers.
There are applications where lightweight hollow shells are required, such as for the fuselage of an airborne vehicle and for a strong but lightweight container. If the combination of a honeycomb sheet with fiber reinforced surface, and foam impregnating the honeycomb and fibrous reinforcing region, could be adapted to a shell part, this would enable the construction of lightweight but strong shells.
In accordance with one embodiment of the present invention, a lightweight reinforced shell part or apparatus is provided, which can be used as part of a shell to hold other apparatus, wherein the shell part is constructed of honeycomb-and-fiber reinforced foam for high strength and low weight. The shell part includes a honeycomb sheet that is bent to have a convex outer surface and concave inner surface, a fibrous reinforcing region at the outer surface, and preferably with a fibrous reinforcing region at the inner surface, with the honeycomb and reinforcing regions being filled with expanded polymer foam. The outer fibrous reinforcing region includes layers of fibrous material with microscopic pores such as those of tissue paper, and preferably with a layer having larger holes such as a woven cloth. The inner reinforcing region has a layer with larger holes such as a woven cloth layer. As a result of manufacturing, there are numerous projections of torn foam at the inner surface of the shell part.
The shell is formed by laying tissue paper against a concave mold wall, laying a cloth over the bottommost tissue paper, laying at least one tissue paper layer over the cloth, and laying honeycomb over the other layers. Then an inner fibrous region is laid on the inside of the honeycomb. Finally, foamable material is placed over the inner fibrous region and the mold is closed.
As the foam expands, it presses the inner fibrous region against the honeycomb to press the honeycomb tightly towards the mold wall and to press the outer fibrous reinforcing region against the mold wall. Foam penetrates everything except some of the tissue paper that lies against the mold wall, to avoid the need to remove foam directly from the mold wall.
The mold is opened so the molded item can be removed, and foam is torn off the molded item. One of the fibrous layers lying at the inner surface of the honeycomb, is a porous Nylon layer or other low surface energy material which is porous and in a layer, which does not stick to foam. This makes it easier to tear away the foam at the outer surface of the Nylon layer. The result is a shell part reinforced through most of its thickness by foam-filled honeycomb, and with the surface region reinforced by fibrous material impregnated by the same quantity of foam. The inner surface of the resulting shell has numerous projections where the foam was torn or cut loose from the cloth layer lying outside the Nylon cloth layer, which shows that the shell was constructed by cutting or tearing away foam.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.